The invention relates to an optical microelectromechanical device, and in particular to an optical MEMS device with improved supports.
U.S. Pat. Nos. 6,574,033, and 6,794,119 disclose optical microelectromechanical systems (optical MEMS) or micro-opto-electromechanical systems (MOEMS) devices comprising arrayed floating reflective members to modulate required images by interference.
FIG. 1A is a cross-section of a display unit of a conventional optical MEMS device 10. In FIG. 1A, the optical MEMS device 10 comprises a conductive layer 13 and a dielectric layer 14 on a glass substrate 12. A reflective layer 18 is supported by a plurality of supporters 16, suspended from the dielectric layer 14 by a predetermined gap d1. The supporters 16 are formed of polymer materials with horizontal extending top portions 162 connecting the reflective layer 18 to improve adhesion therebetween and distribute partial stress when the reflective layer 18 deforms.
As shown in FIG. 1A, a specific wavelength λ1, for example, is constructively enhanced by interference and reflected, with all other wavelengths destructively eliminated by interference when a light beam with multiple wavelengths λ1, λ2, . . . , λn impinges on the reflective layer 18 through the glass substrate 12. The wavelength of the constructive interference depends on the gap d1 between the dielectric layer 14 and reflective layer 18. Furthermore, the reflective layer 18 deforms and descends, attaching to the surface of the dielectric layer 14 as shown in FIG. 1B, when an external actuating current is supplied to the conductive layer 13. Accordingly, the reflectivity of the optical MEMS device 10 is reduced, acting as a “dark” state. Thus, the conventional optical MEMS device 10 with arrayed display units is capable of displaying required images according to external control currents.
FIG. 2A is an enlarged cross-section of a supporter 16 in FIGS. 1A and 1B during fabrication before removing sacrificial layer 15. As shown in FIG. 2A, corresponding to FIGS. 1A and 1B, a plurality of openings 152 perpendicular to the dielectric layer 14 are first defined on the sacrificial layer 15 and filled with fillers, for example, polymers, to form supporters 16 with top portions 162 capable of sustaining bending stress. The thickness, of the top portion 162, and predetermined gap d1, between the dielectric layer 14 and the reflective layer 18, would deteriorate the deforming response time of the reflective layer 18. Because of the opening 152 and restrictions of fabricating processes, the center of the top portion 162, however, sinks seriously when the thickness of the top portion 162 is less than a specific thickness. Simultaneously, the thickness g, the connection between the top portion 162 and post, is reduced, such that the top portion 162 of each supporter 16 may break, reducing reliability of the conventional optical MEMS devices.